Projection type display device

ABSTRACT

A projection type display device includes a light source, a picture information display element, and a light deflection device with a function to deflect light from the light source and irradiate the deflected light on a region of the picture information display element. The light deflection device scans the region on the picture information display element to be irradiated with light over the entire picture information display element within each frame period to thereby project a picture. A picture is displayed by changing the region on the picture information display element irradiated by light within a period of each one frame. The projection type display device provides sharp moving pictures and bright images. Furthermore, the projection type display device provides a wide dynamic range and faithful tone reproducibility for pictures that are mainly dark images. Moreover, the projection type display device can use a Half-V type FLC element for creating bright and sharp moving pictures.

This is a continuation of application Ser. No. 10/690,493, filed on Oct.20, 2003.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an illumination device and a projectiondevice, which are desirable for use in a liquid crystal projector thatwith a projection lens magnifies and projects images from a liquidcrystal display element (i.e., a liquid crystal panel) onto a screen orwall. In particular, the present invention relates to a liquid crystalprojector mainly used to display moving pictures on home theater frontprojectors or rear projection television.

2. Related Background Art

Various types of liquid crystal projectors that illuminate a liquidcrystal panel with a luminous flux from a light source and that with aprojection lens magnify and project pictures from the liquid crystalpanel based on transmitted light or reflected light on a screen or wallhave been suggested in the past, and projectors mainly used fordisplaying moving pictures are being widely sought in order to expandthe market size.

Projectors that have been made public so far belong primarily to tworepresentative types: liquid crystal projectors that use liquid crystaldisplay elements, and projection type display elements (hereinaftercalled “DLP”) based on digital light processing (DLP) that uses adigital mirror device (DMD).

The DLP controls on/off of light by switching at high-speed the angle ofa mirror device built on a semiconductor substrate, which controls theproportion of time in the on state within one frame and thereby achievesa gray scale display (i.e., time-division gray scale). On the otherhand, such time-division gray scale is not used in liquid crystaldisplay elements other than devices that use ferroelectric liquidcrystal. Instead, the liquid crystal display elements utilize a grayscale display method based on analog gray scale, where the value of thevoltage applied to the liquid crystal display element is variedaccording to display picture information in order to display gray scaleinformation.

However, it has become clear from recent research that as long as thetwo types of devices are driven in the conventional manner, the movingpicture high-speed response characteristic that is perceived by humanscannot be obtained from either of them (see “Examination of MovingPicture Quality of Hold, Light Emitting Type Display on an Eight SpeedCRT,” Shuichi Ishiguro and Taiichiro Kurita, Technical Report of IEICEEID 96-4, p. 19).

According to the report, when viewing pictures on a liquid crystaldisplay element, the human eye does not sense that the pictures aredisplayed at high-speed even when the time required for the liquidcrystal to respond is speeded up to infinitely close to zero. The reasonfor this is that the conventional liquid crystal display elements arebased on the so-called “hold type display” principle. This is aphenomenon in which display information enters the observer's eyesconstantly, and the after image effect of eyes causes the pictures tolose sharpness. A “hold type display” is commonly used in a displaymethod that uses the liquid crystal display elements, as well as in amethod of displaying gray scale based on time-division in DLP.

As long as this display method is used, the moving picture displayperformance cannot improve significantly; the research result concludesthat effective methods for improving moving picture quality, to theextent that humans sense that a moving picture is displayed at ahigh-speed, include a method of using a shutter to reduce the timenumerical aperture to 50% or less, and a display method employing doublespeed or higher.

Of the two methods for improving the moving picture quality, the displaymethod employing double speed or higher entails burdening drivecircuits, e.g., requiring complicated picture processing such as pictureinterpolation and requiring even higher speed density such as quad speed(4×) or five speed (5×) in order to obtain a moving picture qualityequivalent to that of CRT, and is therefore not a realistic method forachieving true high-speed display performance.

In contrast, the method of reducing the time numerical aperture by usinga shutter (a so-called “non-hold type display method”) can be realizedfairly easily, since the original picture information can be usedunaltered.

The non-hold type display method developed for direct view type liquidcrystal display elements can be divided into two methods. One is amethod of using high-speed liquid crystal to switch the light on/off,which can be achieved by using ferroelectric liquid crystal or opticallycompensated bend (OCB) mode.

The other method is to turn a backlight on and off. Since this does notrequire the response speed of the liquid crystal to be especiallyhigh-speed, this method can be applied to virtually all liquid crystalmodes.

Since the screen size displayed by a projector is much larger than thatof a direct view type liquid crystal display element, a moving picturequality in the projection type display is sought to be much higher thanthat of the direct view type liquid crystal display element in thefuture. The reason for this is that when the viewing distance remainsthe same, as the screen size becomes larger, the angle between the humaneyes and both ends of the screen becomes larger. As a result, when thesame moving picture is displayed, the angular speed with which picturesmove becomes larger as the screen becomes larger. However, when thenon-hold display method is used on a liquid crystal projector or DLP,the following problems arise:

First, when the method of using high-speed liquid crystal to switch thelight on/off is utilized, the utilization rate of light is determined bythe proportion of the on time, while the utilization rate of lightdeclines considerably according to the proportion of the off time. Thiscan be dealt with fairly easily with direct view type, such as byincreasing the luminance of the backlight, but increasing the luminanceof the light source lamp is difficult with projectors.

Consequently, efforts are underway on projectors to realize a displaythat is even slightly brighter than currently available through acombination of various approaches, such as optics and a display element,in order to increase the utilization rate of light. Due to suchcircumstances, creating off periods through liquid crystal switching isnot a desirable method for projectors, since this would significantlydecrease the utilization rate of light.

In the meantime, the method of turning the backlight on and off is amethod that can be used only on direct view type liquid crystal elementsthat utilize a fluorescent tube; turning a light source on and off isimpossible with halogen lamps that are generally used on projectors.

It has been pointed out that it is difficult to obtain a sharp displayof moving pictures, as well as sufficient dynamic range due to lack ofcontrast in a display element, with conventional projectors. In otherwords, conventional projectors lack moving picture quality and dynamicrange, which are essential factors for achieving vivid visualexpression.

SUMMARY OF THE INVENTION

In view of the above, the present invention relates to a projector thatrealizes a sharp moving picture display based on a non-hold display andwithout significantly sacrificing utilization rate of light.

In accordance with an embodiment of the present invention, a projectiontype display device includes a light source, a picture informationdisplay element, and a light deflection device with a function todeflect light from the light source and irradiate the deflected light onone region of the picture information display element. The lightdeflection device can scan the region on the picture information displayelement to be irradiated with light over the entire picture informationdisplay element within each frame period to thereby project a picture.The picture may be projected on a screen.

In accordance with a preferred embodiment of the present invention, thedisplay element may be line sequentially driven. For example, the linesequential scanning direction may be in a vertical direction of thedisplay element and the light from the light source may be irradiated onthe entire display element in a horizontal direction. The light may beirradiated only a part of the display element in the vertical direction,and the entire element may be irradiated with light by scanning in thevertical direction the region to be irradiated with light in appropriatetiming within each frame period.

In accordance with another preferred embodiment of the presentinvention, the light from the light source irradiates only a part of thedisplay element in the horizontal and vertical directions, and theentire element is irradiated with light by scanning in the horizontaland vertical directions the region to be irradiated with light inappropriate timing within each frame period.

In accordance with another preferred embodiment of the presentinvention, the picture information display element may preferably be aliquid crystal display element, and the liquid crystal display elementis either a reflective type liquid panel or a transmissive type liquidpanel.

The liquid crystal display element may preferably use a liquid crystaldisplay mode having characteristics in which the average molecular axisof the liquid crystal indicates a monostabilized position when novoltage is applied, and the average molecular axis of the liquid crystaltilts to one direction from the monostabilized position at an angleaccording to the magnitude of a voltage of a first polarity applied.

Furthermore, the liquid crystal display element may preferably haveactive elements such as thin film transistors (hereinafter called“TFTs”) and is line, sequentially scanned.

According to another preferred embodiment of the present invention, thepicture information display element is an element that displays pictureinformation by changing the reflecting angle of a mirror surface on eachpixel in order to control the light on/off state.

The light deflection device may be in any format as long as it can varyregions that are irradiated with light. A preferred mode for the lightdeflection device is to use a polygon mirror and to have a function tochange the scanning speed according to display picture information.Furthermore, the light deflection device may preferably have a pictureprocessing function to give picture information signals to the pictureinformation display element according to the scanning speed.

Moreover, the light deflection device may preferably have a function tochange the intensity of the light emitted from the light sourceaccording to the display picture information.

Other objects, features and advantages of the invention will becomeapparent from the following detailed description taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a diagram of the structure of a projection type displaydevice in accordance with a first preferred embodiment of the presentinvention.

FIGS. 2( a) and (b) show timing charts of a drive method for driving theprojection type display device according to the first preferredembodiment of the present invention (timing chart 1).

FIG. 3 shows a picture used in evaluation (picture 1).

FIGS. 4( a) and (b) shows timing charts of a drive method for drivingthe projection type display device in accordance with a preferredembodiment of the present invention (timing chart 2).

FIG. 5 shows a picture used in evaluation (picture 2).

FIGS. 6( a) and (b) show timing charts of a drive method for driving theprojection type display device in accordance with a preferred embodimentof the present invention (timing chart 3).

FIG. 7 shows a diagram of the voltage-transmissivity characteristic of aHalf-V type FLC element.

FIGS. 8( a) and (b) show timing charts of a drive method for driving theprojection type display device in accordance with a preferred embodimentof the present invention (timing chart 4).

FIG. 9 shows a diagram of the structure of a projection type displaydevice in accordance with a second preferred embodiment of the presentinvention.

FIG. 10 shows a timing chart of a drive method for driving theprojection type display device in accordance with the second embodimentof the present invention (timing chart 5).

FIG. 11 shows a timing chart of a drive method for driving theprojection type display device in accordance with the second preferredembodiment of the present invention (timing chart 6)

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1 through 9, preferred embodiments of the presentinvention will be described below.

First, the display principle for a projection type display element inaccordance with a first preferred embodiment of the present embodimentwill be described.

A projection type display device according to the present inventionincludes a light source 1 that is continuously illuminated, a condensingdevice 2, an optical deflection device 3 and a picture informationdisplay element 4, as shown in FIG. 1. The condensing device 2 condensesthe light emitted from the light source 1 to one part of a pictureinformation display element 4, and the optical deflection device 3changes irradiation positions when the condensed light is irradiated ona part of regions of the picture information display element. Imagesprojected by the projection type display device comprising such elementscan be observed when projected on a screen 5. If the display device is arear projection type, the screen 5 is included in the display device; ifthe display device is a front projection type, the screen 5 is separatefrom the display device.

FIG. 1 shows an example in which a polygon mirror is used as a scanningdevice of the deflection device 3, and the rotation direction of thepolygon mirror is indicated as “a.”

Next, a light path of the display device according to the presentinvention will be described. In FIG. 1, arrows labeled A–D indicate alight path. First, the light emitted from the light source 1 follows thelight path A and reaches the condensing device 2, which is shown as aconcave surface mirror in FIG. 1. Next, the condensed light follows thelight path B and reaches the polygon mirror 3, which is the opticaldeflection device. The light reflected from the scanning device followsthe light path C and reaches the display element 4. The light reflectedfrom the display element 4, which is shown as a reflective type displayelement in FIG. 1, follows the light path D to reach the screen 5, whichdisplays the image.

If the configuration allows scanning only in the vertical direction,such as when only one polygon mirror is used as in FIG. 1, the light maybe condensed so that the light is irradiated on the region indicated bya shaded section 6 in FIG. 1, in other words, the light may be condensedin the vertical direction to irradiate only a part of the displayelement 4 but irradiated to spread in the horizontal direction, in orderto irradiate the entire picture information display element 4 using theoptical deflection device 3. This causes the reflected light to displaya region labeled 7 on the screen 5 in FIG. 1, and the entire pictureinformation display element 4 can be irradiated using one-dimensionalscanning by the polygon mirror.

Although a concave surface mirror is used as the condensing device 2 inFIG. 1, the condensing device 2 may be a lens or a combination of amirror and a lens. Furthermore, instead of using a polygon mirror as theoptical deflection device 3, MEMS (Micro-ElectroMechanical Systems) or amethod for rotating a prismatic optical element can be used as a devicefor changing the light path. Although the display element 4 has beendescribed as a reflective type, a transmissive type display element canbe used instead. Moreover, although the screen 5 has been described as arear projection type, a front projection type can be used instead.

Next, referring to FIG. 2, the display by the projection type displaydevice and the timing of the irradiated light scanning will bedescribed. To simplify the description, a projection type liquid crystaldisplay device that uses a nematic liquid crystal display element (e.g.,TN mode) that has analog gray scale displayability will be described.

In FIG. 2( a), the horizontal axis indicates time while the verticalaxis indicates line electrodes, and let us assume that there are linesfrom line 1 to line N in the display element. Each solid line 1indicates the timing at which a gate is selected and the correspondingline is scanned in line sequence from line 1. Line 1 to line N arescanned within a period of one frame, and when the gate selection forthe line N is completed, the process returns to line 1 and repeats.

FIG. 2( b) shows the liquid crystal response and the light irradiationtiming obtained according to the gate selection timing in FIG. 2( a).The liquid crystal completes its response several milliseconds after avoltage is applied. For example, in FIG. 2( b), a little more than halfof one frame time, or approximately 8–10 milliseconds, is spent onresponse. When the response is completed, condensing and scanning takeplace so that light is irradiated in the timing represented by eachshaded area 2.

Next, a description will be made as to why the configuration and thedrive method described above can be used to realize a non-hold displaywithout significantly sacrificing the utilization rate of light.

First, the light source 1 is continuously illuminated, and the lightemitted from the light source 1 is irradiated on the picture informationdisplay element 4 virtually throughout the entire frame period throughthe condensing device 2 and the optical deflection device 3. Thisresults in a utilization rate of light that is considerably highercompared to a method of creating off periods through liquid crystalswitching or a method of creating light and darkness from the lightsource through the rotation of a shutter wheel.

Next, the condensed light is deflected, and the entire display element 4is irradiated within the period of one frame. As a result, any oneregion of the display element 4 experiences a repeating cycle consistingof a period in which it is irradiated with light and a period in whichit is not irradiated with light from the light source 1. On the perpixel level, this results in the realization of the non-hold display.

Furthermore, since the proportion of light irradiation time (i.e., thedisplay duty ratio) within the period of one frame is determined by theextent to which the light condensed by the condensing device 2 can befocused to what area ratio of the display element 4. In other words, thelight to be irradiated on the display element 4 is required to befocused only to a certain extent in order to perform an impulse displaymethod comparable to CRTs, and a sharp and superior moving picturequality can be easily obtained when an analog gray scale element is usedwithout having to employ any special contrivances on the displayelement. On the other hand, when a digital gray scale display elementsuch as DLP is used, since time-division gray scale must be completedwithin the period indicated by each of the shaded areas 2 (i.e., theperiod during which light is irradiated) in FIG. 2( b), for example, aswitching at a higher-speed than in normal devices becomes required.

By changing the scanning speed according to image signals, the dynamicrange of the display element can be substantially expanded. This isdescribed below.

Let us assume that there is image information as shown in FIG. 3. Thisimage shows the sun rising from behind mountains, representing an imagesource that includes complete darkness and the brightness of the sunthat are to be expressed simultaneously. Conventional display elementshave limited dynamic range due to insufficient contrast or luminancecharacteristic and therefore have difficulty expressing realisticimages.

By irradiating light as the scanning speed is varied according to thetiming shown in FIG. 4( b), bright areas can be displayed more brightlyand dark areas can be displayed more darkly, thereby expanding thedynamic range. In other words, shaded areas 2 in FIG. 4( b) indicate thescanning timing of the optical deflection device 3, where the centerregion of the screen that should be displayed brightly is scanned slowlyto provide more luminous flux to the display element 4, while the topand bottom regions of the screen that should be displayed darkly arescanned quickly to reduce the amount of luminous flux provided to thedisplay element 4; this results in a realization of a wide dynamic rangeand provides a vivid image.

In FIG. 3, the part with the sun is scanned slowly by the light source 1in order to express the bright sun, but the mountains may be expressedin a uniform half tone. However, even in the same mountain, the part ofthe mountain that is displayed near selection lines shared by the sun isirradiated with a stronger light, while the part of the mountain that isdisplayed by selection lines different from those of the sun isirradiated with a weaker light. To address this issue, when the scanningspeed of the light source 1 is varied, a picture processing can beperformed to convert the gray scale information according to thescanning speed and optimized image information signals can be providedto the display element 4, which results in displaying a uniform halftone.

Next, FIG. 5 shows an image source that is dark overall. It is an imagein which a dim moon appears in complete darkness. When an attempt toexpress such image information is made on a display element having anarrow dynamic range, light leakage can cause the darkness to beexpressed somewhat brighter, or gray scale blurring at the extreme lowgray scale side can occur; either case makes it impossible to expresssubtle contrast changes in the darkness. In the image shown in FIG. 5,for example, the detailed shape of the dark cloud would not be expressedand would instead be expressed as a single color, resulting in poor tonereprodutioncibility when displayed with low luminance.

However, this problem can be solved with the display element 4 accordingto the present invention by setting an area outside an effective area ofthe display element 4 that is to be irradiated with light by the opticaldeflection control device 3. If there is a large amount of images withdark picture information, it is desirable to set a long period as theperiod for irradiating the area outside the effective display area.

When the average luminance that is irradiated on a screen is low, thescanning that takes place is fast, as shown in FIG. 6( b). As a result,the period indicated by horizontal lines 3 in FIG. 6( b) is a periodduring which light is not irradiated on the screen. In other words, sucha display method is made achieved by having a configuration in which thelight from the light source 1 is irradiated on an area outside theeffective display area of the display element 4. Since the light source1 is continuously illuminated, the light irradiation energy emitted bythe light source 1 remains constant at all times; by having aconfiguration in which the light from the light source 1 is irradiatedon the area outside the effective display area of the display element 4,the light energy that contributes to display can be reduced. As aresult, the problem of having poor display reproducibility at lowluminance does not occur, darkness is expressed as true black, and grayscale blurring at low gray scale does not occur; instead, subtlecontrast changes can be expressed in darkness. It is more desirable toperform picture processing as necessary in these circumstances and togive image information signals according to the amount of lightirradiated on an area outside an effective display area.

To more effectively condense the light from the light source 1, it isdesirable to make the light source 1 itself as close to a point lightsource as possible.

This method can be favorably applied to a ferromagnetic liquid crystal.Typical ferromagnetic liquid crystal is called Half-V type FLC and iscapable of displaying images at high-speed and in analog gray scale; forthis reason, its application to high-speed displayable liquid crystaltelevision and full-color display methods utilizing color mixtures basedon time-division is anticipated.

A representative example of the voltage-transmissivity characteristic ofa Half-V type FLC element is shown in FIG. 7. Due to the fact that whilethe transmissivity changes drastically in response to voltage in onepolarity, the transmissivity undergoes little change in response tovoltage in the opposite polarity, a non-hold display using light on/offthrough liquid crystal switching can be realized by a simple alternatingcurrent drive. For this reason, the Half-V type FLC is considered aneffective display mode for direct view type liquid crystal television.

With the picture information display element according to the presentinvention, scanning by the optical deflection control device 3 with theirradiated light and adjusting as necessary the timing of voltageapplication to the Half-V type FLC element make it possible to restrainany significant decline in the utilization rate of light, which resultsin achieving both a bright display and a sharp moving picture quality.

Next, a description will be made as to an example of the liquid crystaldisplay device according to the present invention applied to a Half-Vtype FLC element. FIG. 8( a) shows scanning of scanning lines on aliquid crystal element. As shown in this drawing, the Half-V type FLCelement performs a line sequential drive to divide each frame into twosubfields, namely a write field and an erase field, in order to repeatwriting and erasing.

In the meantime, FIG. 8( b) is a timing chart of the light sourcescanning, where thick lines 2 in FIG. 8( b) indicate that the light fromthe light source is deflected to change the irradiation positions. Toscan with light source deflection as shown in this drawing, an area invicinity of the leading line is irradiated virtually simultaneously orslightly after a selection signal for writing is applied to a leadingline gate. Furthermore, an area in vicinity of the final line isirradiated with a condensed light slightly before a selection signal forerasing is applied to the final line gate. As a result, the energy ofthe light emitted by the light source can be used for display on thescreen with virtually no waste. Furthermore, expanding the dynamic rangeby varying the scanning speed and faithfully reproducing a dark pictureby providing a period to irradiate the light to an area outside aneffective display area are also applicable to the Half-V type FLCelements, as in the earlier discussion.

Next, referring to FIG. 9, a description will be made as to a projectiontype display element in accordance with a second preferred embodiment ofthe present invention through a discussion similar to the above.

A projection type display device according to the present inventionincludes a light source 1 that is continuously illuminated, a condensingdevice 2, optical deflection devices 3 and 4 and a picture informationdisplay element 5, as shown in FIG. 9. The condensing device 2 condensesthe light emitted from the light source 1 to one part of the pictureinformation display element 5, and the optical deflection devices 3 and4 change irradiation positions when the condensed light is irradiated ona part of regions of the picture information display element 5. Imagesprojected by the projection type display device having such elements canbe observed when projected on a screen 6. If the display device is arear projection type, the screen 6 is included in the display device; ifthe display device is a front projection type, the screen 6 is separatefrom the display device.

FIG. 9 shows an example in which a polygon mirror 4 and a simpleharmonic motion mirror surface body 3 are used as a scanning device, andtheir rotation directions are indicated as “a” and “b,” respectively.

Next, the light path of the display device according to the presentinvention will be described. In FIG. 9, arrows labeled A–E indicate alight path. First, the light emitted from the light source 1 follows thelight path A and reaches the condensing device 2, which is shown as aconcave surface mirror in FIG. 9. Next, the condensed light follows thelight path B and reaches the optical deflection device 3, which isdescribed as the simple harmonic motion mirror surface body in FIG. 9,and follows the light path C to reach the optical deflection device 4,which is described as the polygon mirror. The light reflected from theoptical deflection device 4 follows the light path D and reaches thedisplay element 5. The light reflected from the display element 5, whichis shown as a reflective type display element in FIG. 9, follows thelight path E to reach the screen 6, which displays the image.

Unlike the example in FIG. 1 where only one polygon mirror is used, atwo-dimensional, horizontal and vertical scanning can be done in theexample shown in FIG. 9; for this reason, the light may be condensed sothat the light is irradiated on a region indicated by a shaded section 7on the picture information display element 5 in FIG. 9. In other words,the light may be condensed in the vertical and horizontal directions toirradiate only a part of the display element 5, in order to irradiatethe entire picture information display element 5 with the opticaldeflection devices 3 and 4. This causes the reflected light to display aregion labeled 8 on the screen 6 in FIG. 9, and the entire pictureinformation display element 5 can be irradiated using two-dimensionalscanning by the optical deflection devices 3 and 4.

Although a concave surface mirror is used as the condensing device 2 inFIG. 9, it may be a lens or a combination of a mirror and a lens, as inFIG. 1. Furthermore, instead of using the elements in FIG. 9 as theoptical deflection device 3 and 4, MEMS or a method for rotating aprismatic optical element can be used as a means for changing lightpaths. Although the display element 5 is described as a reflective type,a transmissive type display element can be used instead. Moreover,although the screen 6 has been described as a rear projection type, afront projection type can be used instead.

Next, referring to FIG. 10, a description will be made as to the displayby the projection type display device and the timing of the irradiatedlight scanning. To simplify the description, a projection type liquidcrystal display device that uses a nematic liquid crystal displayelement (e.g., TN mode) that has analog gray scale displayability willbe described.

In FIG. 10, the horizontal axis indicates time while the vertical axisindicates line electrodes, and let us assume that there are gate linesfrom line 1 to line N in the display element. Here, let us assume atiming for gate selection similar to the timing in FIG. 2( a), and thelines are scanned in line sequence from line 1 to line N to form oneframe. Line 1 to line N are scanned within a period of one frame, andwhen the gate selection for the line N is completed, the process returnsto line 1 and repeats.

In FIG. 10, a shaded section labeled A indicates the location and timingof light irradiation. As in FIGS. 2( a) and (b), the light irradiationon the display element takes place after a gate is selected, a signalvoltage is applied to a liquid crystal layer, and the response by theliquid crystal is completed. First, the pixel in the first row, firstcolumn, or a region including its vicinity, is irradiated. Next, theoptical deflection control device 3 and 4 in FIG. 9 are controlled asnecessary in order to follow the direction of an arrow B in FIG. 10 toirradiate the entire display element.

With this method, a high utilization rate of light and a non-holddisplay can be realized based on a discussion similar to the one givenfor FIG. 2.

Furthermore, the dynamic range of the display element can beconsiderably expanded by varying the scanning speed according to imagesignals, as in the first preferred embodiment. Moreover, the secondpreferred embodiment can also be applied to the Half-V type FLC based ona discussion similar to the one given for the first preferredembodiment.

The liquid crystal display element may be either reflective ortransmissive type.

The reflective type has an advantage in that it can be miniaturized,while the transmissive type has an advantage of easy designing of theoptics. The color display method may be based on the use of colorfilters or on separating the light from the light source into the threeprimary colors RGB using a dichroic mirror and using a three-panelliquid crystal display element. Or, a field sequential color method thatutilizes color mixtures based on time-division may be used.

Various methods can be considered as a method for scanning withcondensed light, such as a method of rotating a polygon mirror, MEMS,and a method of rotating a prismatic optical element, but the polygonmirror is the favorable one in terms of lowering cost.

Although the luminous flux emitted by a light source has been describedas being constant at all times since it is difficult to performhigh-speed modulation on luminous flux emitted by such light sources ashigh luminance halogen lamps, the luminous energy can be varied within aperiod of one frame by using such light sources as a high luminance LEDor laser that has high response speed; with these, the luminous fluxdivergence amount can be varied depending on the scanning timing orpicture information signal.

As described earlier, a sharp moving picture quality based on a non-holddisplay and a bright display can both be obtained by configuring theprojection type display device as described. In addition, by controllingthe scanning speed, a wider dynamic range and faithful reproduction ofdark pictures can be realized. Furthermore, by applying theconfiguration according to the present embodiment to a Half-V type FLCelement, which conventionally was not necessarily considered favorablefor projector use, a bright display element that does not sacrifice theutilization rate of light can be realized.

As described above, according to the present invention, by configuring aprojection type display device comprising a device to condense a lightemitted from a light source to one part of a display panel and a deviceto deflect the condensed light, a sharp moving picture quality based ona non-hold display and a bright display can both be obtained. Inaddition, by controlling the scanning speed through light sourcedeflection, a wider dynamic range and faithful reproduction of darkpictures can be realized. Furthermore, by applying the configurationaccording to the present embodiment to a Half-V type FLC element, whichconventionally was not necessarily considered favorable for projectoruse in terms of effective utilization of light source, a bright displayelement that does not sacrifice the utilization rate of light can berealized.

The following is a description of the present invention in furtherdetail based on embodiment examples.

Embodiment Example 1

A projection type liquid crystal display device was built using theoptics described in the first preferred embodiment. The cell used was anactive matrix type VGA (640×480) liquid crystal element, 1 inch diagonal(0.6 inch vertical×0.8 inch horizontal). The liquid crystal element wasa reflective type liquid crystal element whose reflecting electrode wason the active matrix substrate side and the counter electrode was atransparent electrode. The liquid crystal used in the reflective typeliquid crystal element was a so-called TN mode, which is a mode in whichthe half tone display state is determined not by the polarity of thevoltage applied but by the absolute value level of the voltage applied,as a characteristic of nematic liquid crystal.

A polygon mirror was used as an element for light source scanning. Ahalogen lamp was used as a light source, so that the light emitted fromthe light source traveled via the polygon mirror and was condensed by alens on a region defined by 5 mm vertical (but the entire region in thehorizontal direction) of the liquid crystal panel.

The projection type liquid crystal display device thus obtained wasdisplayed according to the timing described in FIG. 2, and the movingpicture quality was evaluated.

The evaluation of the moving picture quality was a subjective evaluationby approximately 10 non-experts and made on a scale of 1 to 5 (grade),whose definitions are described below. The pictures used in theevaluation were three types (a skin tone chart, a sightseeing sign, anda yacht harbor) from BTA's high definition standard pictures (stillimages), and 432×168 pixels were cut out from the center part of eachfor use in the evaluation.

Next, these pictures were made to move at a constant speed of 6.8deg/sec, which is the common moving speed for television programs, tocreate moving pictures, and the blurring of the pictures was evaluated:

-   -   Grade 5: No blurring on the periphery of the screen at all,        sharp and excellent moving picture quality.    -   Grade 4: Blurring on the periphery of the screen almost not        noticeable.    -   Grade 3: Blurring on the periphery of the screen observed, and        small characters are difficult to recognize.    -   Grade 2: Blurring on the periphery of the screen prominent, and        even large characters are difficult to recognize.    -   Grade 1: Blurring prominent over the entire screen, and the        original picture is almost unrecognizable.

The output from the picture source computer was at a picture rate of 60frames per second in progressive scanning.

The result indicated that no blurring was observed on the periphery ofthe moving pictures at all. Subjective evaluation of the degree ofblurring on the periphery was 5 on a scale of 1 to 5. Furthermore, itwas confirmed that a satisfactorily bright display was obtained.

When the evaluation was done using a general CRT, all evaluators gave 5,which is excellent, on a scale of 1 to 5; when the evaluation was donewith a liquid crystal projector using normal optics and with the sameliquid crystal used in the present embodiment example, the evaluationresults were 2–3 on a scale of 1 to 5.

Embodiment Example 2

The liquid crystal display device described in the embodiment example 1was used for display. The picture used in this case was an image of thesun rising from behind dark mountains, as shown in FIG. 3. In this case,a display in which the scanning speed was varied according to pictureinformation (evaluation picture 1), as in FIG. 4, and a display in whichthe scanning speed remained constant at the scanning speed shown in FIG.2 (evaluation picture 2), as in the scanning in the embodiment example1, were compared.

The result indicated that the evaluation picture 1 had striking contrastbetween dark and bright areas and therefore successfully realized avivid image. On the other hand, the evaluation picture 2 gave animpression of slightly lacking contrast. The evaluation picture 1 hadslight luminous unevenness on the surface of the mountains, but when aninformation signal with picture processing that took into considerationthe amount of light irradiated was provided, the result was a naturaland vivid image with no display luminous unevenness.

Embodiment Example 3

The liquid crystal display device described in the embodiment example 1was used for display. The polygon mirror was altered from the embodimentexample 1 and set to irradiate light on an area outside an effectivedisplay area. The picture used for display in the present embodimentexample was a dark image of a dim moon appearing in complete darkness,as in FIG. 5. A display in which a light source scanning was performedso that a period for irradiating an area outside the effective displayarea was provided within one frame and other periods were used fordisplay (evaluation picture 3), as shown in FIG. 6, and a display inwhich the light source scanning speed remained constant (evaluationpicture 4), as in the scanning according to the embodiment example 1,were compared.

The result indicated that although subtle contrast differences in anextremely dark picture were faithfully reproduced in the evaluationpicture 3, the evaluation picture 4 gave the impression of slightlylacking darkness in black areas and insufficient gray scale resolutionat low gray scale.

Embodiment Example 4

The liquid crystal material and the orientation processing method usedin the liquid crystal element were altered to build a liquid crystaldisplay device similar to the one in the embodiment example 1. Thefollowing is a description of the procedure:

Preparation of a Liquid Crystal Composition:

First, the following liquid crystal compounds were mixed according tothe weight ratio indicated to the right of each compound, and a liquidcrystal composition LC-1 was prepared.

The physical parameters of the liquid crystal composition LC-1 are asfollows:

-   -   86.3 61.2 −7.2

-   Phase transition temperature (° C.): ISO.→Ch→SmC*→Cry

-   Spontaneous polarization (30° C.): Ps=2.9 nC/cm²

-   Cone angle (30° C.): θ=23.3° (100 Hz, ±12.5V, substrate gap 1.4 μm)

-   Spiral pitch in SmC*phase (30° C.): 20 μm or more    Making a Liquid Crystal Cell:

Substrates similar to the ones in the embodiment example 1 were used. Acommercially available TFT liquid crystal orientation film (SE7992 byNissan Kagaku) was coated as orientation control films based on a spincoat method to a film thickness of 150 Å each. Orientation control films6 a, 6 b were rendered a rubbing processing (uniaxial orientationprocessing) with cotton cloths. For the rubbing processing, a rubbingroll 10 cm in diameter and with cotton cloths affixed on its outerconference surface was used; the stuffing amount was 0.7 mm, the feedrate was 10 cm/sec, the number of revolutions was 1000 rpm, and thenumber of feeds was 4. The rubbing direction was set to make both thetop and bottom substrates parallel with the source line.

Next, silica beads (spacers) with average particle size of 1.5 μm werescattered on one of the substrates; the substrates were affixed so thatthe rubbing processing direction on one of the substrates wasanti-parallel to the rubbing processing direction of the other; and acell with uniform substrate gaps was obtained.

The liquid crystal composition LC-1 was poured at the Ch phasetemperature into the cell made through the process described above; thecell with the liquid crystal composition LC-1 was cooled to atemperature at which the liquid crystal indicated a chiral smecticliquid crystal phase (however, the cooling rate was 1° C./min); and a+5V offset voltage (direct current voltage) was applied when the liquidcrystal's phase transitioned from the Ch phase to the SmC* phase (withinthe temperature range of Tc−2° C. through Tc+2° C.).

Next, a liquid crystal panel P1 was actually driven and its movingpicture quality was evaluated. For this, the picture display was basedon the timing chart shown in FIG. 8. As a result, in the subjectiveevaluation of the degree of blurring on the periphery, as in theembodiment example 1, 5 was given on a scale of 1 to 5. In addition, itwas confirmed that satisfactorily bright display was obtained.

When the liquid crystal element was applied to a conventional liquidcrystal projector that does not use light source scanning, thesubjective evaluation of the degree of blurring on the periphery was 4or 5 on a scale of 1 to 5, which is a slightly inferior result of amoving picture quality to the moving picture quality obtained withscanning, and a bright display could not be obtained since thebrightness was reduced by half.

Embodiment Example 5

Using the cell configuration in the embodiment example 4, an experimentto vary the light source scanning speed according to picture informationand to provide a period for irradiating an area outside an effectivedisplay area, as in embodiment examples 2 and 3, was conducted. As aresult, it was confirmed that results similar to those gained in theembodiment examples 2 and 3 could be obtained.

Embodiment Example 6

A projection type liquid crystal display device using the opticsdescribed in the second preferred embodiment was built. The cell usedwas the same as in the display device in the embodiment example 1.

Two polygon mirrors were used as elements for light source scanning, sothat optics in which the light source can be scanned in two axialdirections, vertical and horizontal, was obtained. A halogen lamp wasused as a light source, so that the light emitted from the light sourcetraveled via the polygon mirrors and was condensed by a lens on a regiondefined by 5 mm vertical×5 mm horizontal of the liquid crystal panel.

The projection type liquid crystal display device thus obtained wasdisplayed according to the timing shown in FIG. 11, and the movingpicture quality was evaluated as in the embodiment example 1.

The result indicated that no blurring was observed on the periphery ofthe moving pictures at all. Subjective evaluation of the degree ofblurring on the periphery was 5 on a scale of 1 to 5. Furthermore, itwas confirmed that a satisfactorily bright display was obtained.

Embodiment Example 7

The display device used in the embodiment example 6 was used to conductan experiment to vary the scanning signal according to picture signals,as in embodiment examples 2 and 3. As a result, it was confirmed that awide dynamic range as in the embodiment examples 2 and 3 could beobtained.

Embodiment Example 8

The liquid crystal material and the orientation processing method usedin the liquid crystal element were replaced with those used in theembodiment example 4, and a liquid crystal display device similar to theone in the embodiment example 6 was built. As a result, it was confirmedthat excellent results both in the moving picture quality and brightnesscould be obtained, as in the embodiment example 4. In addition, when thescanning speed was varied according to the picture signal on thisdisplay device, as in the embodiment example 5, results similar to thosein the embodiment example 7 were obtained.

While the description above refers to particular embodiments of thepresent invention, it will be understood that many modifications may bemade without departing from the spirit thereof. The accompanying claimsare intended to cover such modifications as would fall within the truescope and spirit of the present invention.

The presently disclosed embodiments are therefore to be considered inall respects as illustrative and not restrictive, the scope of theinvention being indicated by the appended claims, rather than theforegoing description, and all changes which come within the meaning andrange of equivalency of the claims are therefore intended to be embracedtherein.

1. A projection type display device comprising: a light source; apicture information display element having a plurality of scanning lineswhich are driven line-sequentially; and a light deflection device with afunction to deflect light from the light source and irradiate thedeflected light on one region of the picture information displayelement, wherein the light deflection device scans the region on thepicture information display element to be irradiated with light over anentire region of the picture information display element within eachframe period to thereby project a picture, and wherein the lightirradiated on the picture information display element is scanned at ascanning speed faster than a scanning speed of the plurality of scanninglines.
 2. A projection type display device according to claim 1, whereinthe scanning lines are driven at different timings to change the regionto be irradiated by the light so that the region is irradiated after aresponse time from the voltage application by the scanning lines.
 3. Aprojection type display device according to claim 1, further comprisingmeans to change a scanning speed of the light deflection deviceaccording to display picture information.
 4. A projection type displaydevice according to claim 1, further comprising a picture processingfunction to change a scanning speed of the light deflection device andgive a picture information signal to the picture information displayelement according to the scanning speed.